The primary objective of our research project i to elucidate the mechanism by which cholesterol synthesis is brain is regulated during and after development. In order to identify the enzymatic reactions that show age dependent alterations and thereby become rate limiting for cholesterol synthesis in brain, we have investigated in our earlier studies the activities of mevalonate kinase, phosphomevalonate kinase, pyrophosphomevalonate decarboxylase and HMG CoA synthase in brain S105 at various stages of development. We reported that decarbosylation of pyrophosmevalonate and the activity of HMG CoA synthase in brain may serve as regulatory steps in cholesterol synthesis. We plan to assay brain S105 at various stages of development for the activities of the following enzymes: HMG, HMG CoA lyase, isopentenyl pyrophosphate isomerase, dimethylallyl transferase and pyrophosphatase(s). We also plan to purify HMG CoA synthase in brain and compare the properties of brain enzzme with the enzyme in liver. Another aim of this project is to study the role of cholesterol esters and cholesterol ester metabolizing enzymes in the processes of myelination and demyelination. To attain this objective we recently examined the properties and subcellular distribution of cholesterol metabolizing enzymes in human brain and also compared the levels in various diseased conditions. We reported that the properties and subcellular distribution of cholesterol esterifying enzyme in human brain are similar to those in rat brain, but that hydrolase(s) in human brain differ from those in rat brain in several respects. During the current project period we plan to compare the relative rates of hydrolysis of cholesterol esters of different fatty acids by hydrolase(s) in brain. Cerebrospinal fluid that bathes the brain is a convenient material for assessing the homeostasis of the brain tissue. During the current project period we will attempt to determine whether cholesterol ester synthesizing enzyme in brain which utilizes free fatty acid as substrate is also present in human cerebrospinal fluid.